Engineering Commons^™

Prediction Interval Estimation Techniques For Empirical Modeling Strategies And Their Applications To Signal Validation Tasks, Brandon Peter Rasmussen

Doctoral Dissertations

The basis of this work was to evaluate both parametric and non-parametric empirical modeling strategies applied to signal validation or on-line monitoring tasks. On-line monitoring methods assess signal channel performance to aid in making instrument calibration decisions, enabling the use of condition-based calibration schedules. The three non-linear empirical modeling strategies studied were: artificial neural networks (ANN), neural network partial least squares (NNPLS), and local polynomial regression (LPR). These three types are the most common nonlinear models for applications to signal validation tasks. Of the class of local polynomials (for LPR), two were studied in this work: zero-order (kernel regression), and …

Analytical Modeling Of High Performance Reconfigurable Computers: Prediction And Analysis Of System Performance., Melissa C. Smith

Doctoral Dissertations

The use of a network of shared, heterogeneous workstations each harboring a Reconfigurable Computing (RC) system offers high performance users an inexpensive platform for a wide range of computationally demanding problems. However, effectively using the full potential of these systems can be challenging without the knowledge of the system’s performance characteristics. While some performance models exist for shared, heterogeneous workstations, none thus far account for the addition of Reconfigurable Computing systems. This dissertation develops and validates an analytic performance modeling methodology for a class of fork-join algorithms executing on a High Performance Reconfigurable Computing (HPRC) platform. The model includes the …

Monte Carlo Simulation Of Neutron Detectors, Andrew Curtis Stephan

Doctoral Dissertations

Neutron detectors are simulated using Monte Carlo methods in order to gain insight into how they work and optimize their performance. Simulated results for a Micromegas neutron beam monitor using a custom computer code are compared with published experimental data to verify the accuracy of the simulation. Different designs (e.g. neutron converter material, gas chamber width, gas pressure) are tested to assess their impact on detector performance. It is determined that a ¹⁰B converter foil and 1 mm drift gap width work best for a neutron beam monitor. The Micromegas neutron beam monitor neutronics are evaluated using the computer …

Numerical Simulation Of Separating Flows Using Computational Models Based On The Vorticity Confinement Method, Lesong Wang

Doctoral Dissertations

The objective of the present research is to investigate the recent development of the vorticity confinement method. First, a new formulation of the vorticity confinement term is studied. Advantages of the new formulation over the original one include the ability to conserve the momentum, and the ability to preserve the centroid motion of some flow properties such as the vorticity magnitude. Next, new difference schemes, which are simpler and more efficient than the old schemes, are discussed. At last, two computational models based on the vorticity confinement method are investigated. One of the models is devised to simulate inviscid flows …

Transportation Shortest Path Search Area Model, Hui Wang

Doctoral Dissertations

Although many studies on shortest-path algorithms have been conducted in the past, few of them have considered the time and effort required to obtain and update the weight property of the network arcs. For transportation-related problems – due to the size and complexity of the network – preparing, updating, and transmitting the network database on which the shortest-path algorithms perform can be a challenge.

This study designed a Transportation Shortest Path Search Area (TSPSA) model to enhance the database preparation and updating step before any shortest-path search algorithm can start processing. Taking advantage of the characteristics of the transportation networks, …

Thermography Detection On The Fatigue Damage, Bing Yang

Doctoral Dissertations

It has always been a great temptation in finding new methods to in-situ “watch” the material fatigue-damage processes so that in-time reparations will be possible, and failures or losses can be minimized to the maximum extent. Realizing that temperature patterns may serve as fingerprints for stress-strain behaviors of materials, a state-of-art infrared (IR) thermography camera has been used to “watch” the temperature evolutions of both crystalline and amorphous materials “cycle by cycle” during fatigue experiments in the current research.

The two-dimensional (2D) thermography technique records the surface-temperature evolutions of materials. Since all plastic deformations are related to heat dissipations, thermography …

Effects Of Environment And Frequency On The Fatigue Behavior Of The Spallation Neutron Source (Sns) Target Container Material - 316 Ln Stainless Steel, Hongbo Tian

Doctoral Dissertations

As the candidate target container material of the new Spallation Neutron Source (SNS) being designed and constructed at the Oak Ridge National Laboratory (ORNL), 316 low-carbon nitrogen-added (LN) stainless steel (SS) will operate in an aggressive environment, subjected to intense fluxes of high-energy protons and neutrons while exposed to liquid mercury. The SNS is an accelerator-based neutron source that provides pulsed beams of spallation neutrons by bombarding a mercury target with 1 GeV protons. The function of the SNS is to convert a short pulse (< 1 ms, 60 Hz, 17 kJ/pulse), high-average-power (1 MW), 1-GeV proton beam into 18 lower-energy (< 1eV), short-pulsed (~ tens of ms) neutron beams optimized for use by neutron-scattering instruments.

The current project is oriented toward materials studies regarding the effects of test environment …

Directional Solidification, Microstructures And Mechanical Properties Of Cr-Cr3si Eutectic Alloys, Hongbin Bei

Doctoral Dissertations

Alloys based on intermetallics have been considered for high temperature structural applications. However, many of these alloys suffer from intrinsic brittleness and low fracture toughness at ambient temperature. Therefore, ductile-phase-toughened intermetallic composites are being investigated as a means to improve the fracture toughness. A subset of this class of materials is in-situ composites produced by directional solidification of intermetallic eutectics. In this study, the Cr-Cr₃Si eutectic system is selected as a model system to investigate composites by directional solidification, where the strong, but brittle Cr₃Si is combined with a more ductile Cr-rich solid solution.

A series …

Integrated Field Emission Electron Guns With Single Vertically Aligned Carbon Nanofiber Cathodes, Michael Alberto Guillorn

Doctoral Dissertations

Nanostructured carbon-based materials hold great promise as field emission (FE) cathodes for integrated FE devices. These materials display remarkable FE properties as a consequence of their unique chemical and physical properties. Among this class of materials, the vertically aligned carbon nanofiber (VACNF) is exceptional in that its synthesis can be deterministically controlled. This has enabled the characterization of the FE properties of individual VACNF grown on Si substrates. The results of these studies indicate that the VACNF is an excellent candidate for integrated FE electron sources where the generation of a focused electron beam from a microscale structure is required. …

Polymer-Based Capacitors, Junction Field -Effect Transistors, And A Follower Circuit By Lithography, Self -Assembly, And Ink -Jet Printing Techniques, Yuxin Liu

Doctoral Dissertations

The study of organic materials to create field-effect transistors has recently emerged and is gaining much interest. All-polymer electronic devices are currently in their infancy, like semiconductor devices when they first appeared. As a result, current performance of these devices is in no way comparable to the state-of-the-art semiconductor devices. However, all-polymer devices have a few possible appealing advantages. First, all polymer devices have the potential for low-cost fabrication due to their ease of manufacturability, with fewer and simpler processing steps compared with solid-state semiconductor devices. Secondly, polymer devices offer the ability of material flexibility. Lastly, polymer devices may prove …

Assessment And Redesign Of The Synoptic Water Quality Monitoring Network In The Great Smoky Mountains National Park, Kenneth Ray Odom

Doctoral Dissertations

The purpose of this study was to assess and redesign an existing 83-site synoptic water quality monitoring network in the Great Smoky Mountains National Park. The study involved a spatial analysis of water quality data (pH, ANC, conductivity, chloride, nitrate, sulfate, sodium, and potassium), watershed characteristics (geology, morphology, and vegetation), and collocated site information to determine which sites were redundant and a temporal analysis to determine the effectiveness of the current sampling frequency to detect long-term trends. The spatial analysis employed a simulated annealing algorithm using the variable costs of the network and the results of multivariate data techniques to …

Detecting Changes In Global Dynamics With Principal Curves And Information Theory, Sandeep Rajput

Doctoral Dissertations

Two approaches to characterize global dynamics are developed in this dissertation. In particular, the concern is with nonlinear and chaotic time series obtained from physical systems. The objective is to identify the features that adequately characterize a time series, and can consequently be used for fault diagnosis and process monitoring, and for improved control.

This study has two parts. The first part is concerned with obtaining a skeletal description of the data using Cluster-linked principal curves (CLPC). A CLPC is a non-parametric hypercurve that passes through the center of the data cloud, and is obtained through the iterative Expectation-Maximization (E-M) …

Impacts Of Environmental Factors On Flexible Pavements, Gang Zuo

Doctoral Dissertations

Mechanistic-empirical pavement design methods for flexible pavements are based on the assumption that the pavement life is inversely proportional to the magnitude of the traffic-induced pavement strains. These strains vary with the stiffness of the asphalt layer and underlying base layer and subgrade. Environmental factors, such as the temperature in the asphalt concrete layer and the water content in the base layer and the subgrade, have a significant impact on the stiffness of relevant layers in pavement systems, and consequently the estimated life of flexible pavements. A comprehensive instrumentation system was installed at four sites across the state of Tennessee …

Probabilistic Based Design Of Frp Structures, Maha Khader Alqam

Doctoral Dissertations

This thesis presents the results of an analytical probabilistic based design procedure for concentrically loaded compression members and simply supported beams of fiber-reinforced polymeric (FRP) composite materials. Resistance factors for use in an LRFD format are developed for columns for both flexural buckling and local buckling of doubly symmetric sections, both flexural buckling and flexural-torsional buckling of equal leg angles, and material failure. Resistance factors are developed for lateral-torsional buckling of simply supported doubly symmetric beams loaded with concentrated vertical loads at mid-spans. The developed resistance factors are a function of the coefficient of variation of the appropriate material properties. …

Topics In Graph Algorithms: Structural Results And Algorithmic Techniques, With Applications, Faisal Nabih Abu Khzam

Doctoral Dissertations

Coping with computational intractability has inspired the development of a variety of algorithmic techniques. The main challenge has usually been the design of polynomial time algorithms for NP-complete problems in a way that guarantees some, often worst-case, satisfactory performance when compared to exact (optimal) solutions. We mainly study some emergent techniques that help to bridge the gap between computational intractability and practicality. We present results that lead to better exact and approximation algorithms and better implementations. The problems considered in this dissertation share much in common structurally, and have applications in several scientific domains, including circuit design, network reliability, and …

Rheology Of Lyocell Solutions From Different Cellulosic Sources And Development Of Regenerated Cellulosic Microfibers, Zuopan Li

Doctoral Dissertations

The primary goals of the study were to develop manufactured cellulosic fibers and microfibers from wood pulps as well as from lignocellulosic agricultural by-products and to investigate alternative cellulosic sources as raw materials for lyocell solutions. A protocol was developed for the lyocell preparation from different cellulose sources. The cellulose sources included commercial dissolving pulps, commercial bleached hardwood, unbleached hardwood, bleached softwood, unbleached softwood, bleached thermomechanical pulp, unbleached thermomechanical pulp, bleached recycled newsprint, unbleached recycled newsprint, bagasse and kudzu.

The rheological behavior of solutions was characterized. Complex viscosities and effective elongational viscosities were measured and the influences of parameters such …

A Distributed Control System For Priority-Based Site-Specific Irrigation, Fabio Rodrigues De Miranda

Doctoral Dissertations

Site-specific irrigation enables maximizing yields and water use efficiency for fields with variation in soil water availability. Distributed control for fixed irrigated systems, with controllers close to the sensors and actuators in the field, is easier to install and maintain, and less susceptible to damage by lightning strikes compared to centralized control, but is only economically viable with affordable, low-power controllers. A low cost, solar-powered, feedback irrigation controller for distributed control of fixed irrigation systems was developed and tested. The system used soil water potential measurements to control the amount of water applied to each specific zone of a field. …

Delineation Of Management Units For Site-Specific Irrigation.”, Carlos Wagner Oliveira

Doctoral Dissertations

Variability of soil properties in many fields is too great for a whole field to be effectively managed with a uniform application of irrigation water. Consequently, a decision must be made for irrigation management about which areas in the field should be treated differently or grouped. A decision-making framework was developed to determine whether site-specific irrigation management would be cost effective for selected fields. The framework is designed to find the best field layout in terms of water management, and tests the hypothesis that there is a particular field management layout that maximizes net return. As part of the framework, …

Anisotropic Adaptation On Unstructured Grids, Guoping Xia

Doctoral Dissertations

The efficient representation of the highly directional features in a flow field with adapted anisotropic grids forms the focus of the analysis. Anisotropic adaptation is more effective than isotropic adaptation and requires more degrees of freedom from the mesh, which also demands the use of unstructured grids in the adaptation. The size and orientation of an anisotropic element require a matrix-like local feature indicator. The Hessian, a matrix composed of the second derivatives of an appropriate flow variable, is defined and used as a feature indicator in the adaptation. The Hessian provides a metric that defines the length of an …

Learning From Data With Localized Regression And Differential Evolution, Mark A. Buckner

Doctoral Dissertations

Learning from data is fast becoming the rule rather than the exception for many science and engineering research problems, particularly those encountered in nuclear engineering. Problems associated with learning from data fall under the more general category of inverse problems. A data-drive inverse problem involves constructing a predictive model of a target system from a collection of input/output observations. One of the difficulties associated with constructing a model that approximates such unknown causes based solely on observations of their effects is that collinearities in the input data result in the problem being ill-posed. Ill-posed problems cause models obtained by …

Molecular Modeling At Interfaces: Phase Equilibria Of Complex Fluids, And Mechanical Properties Of Nanostructures, Jose L. Rivera-Rojas

Doctoral Dissertations

Molecular simulation is a very powerful technique that allows us to predict thermodynamic and transport properties of bulk and confined phases, as well as phase equilibria and interfacial properties. These properties are often crucial to the design of chemical and related industrial processes. Molecular simulation can predict these properties over a wide range of conditions, in contrast with experiments, which at extreme conditions (e.g., high temperature and/or high pressure) are often very difficult and in some cases dangerous. Furthermore, semi-empirical and empirical engineering models can frequently only be used for the specific systems to which they are fitted – that …

Design And Fabrication Of A Microscale Joule -Thomson Refrigerator, Lionel Gamini Hewavitharana

Doctoral Dissertations

A simple thermodynamic, heat transfer, and fluid flow model was developed for microscale Joule-Thomson refrigerators (JT devices). For a given geometry, the model predicted that the cooling capacity of the refrigerator increased with the inlet refrigerant pressure. The effectiveness of the JT device also increased with the inlet pressure, and the heat exchanger channel length. At a constant inlet pressure, the effectiveness, and the refrigeration capacity of a given JT device increased as the aspect ratio of heat exchanger channels was increased. For nitrogen refrigerant, the model predicted that it was possible to obtain approximately 250 mW of refrigeration capacity …

Effects Of Diabetes And Aging On Posture And Acceleration Thresholds During Lateral Translations, Samantha Jean Richerson

Doctoral Dissertations

Research objectives. One source of falls in the elderly may be an inability to sufficiently adjust to transient postural perturbations or slips. Identifying useful predictors of fall potential, as well as factors that affect the ability of an individual to detect a movement of the standing support surface may provide insight into postural stability and methods to increase stability in elders. To do this, acceleration thresholds to short, precise, lateral platform translations and the resultant psychophysical responses of adults with early Type 2 diabetes to age-matched controls and young adults were measured.

Methods. Using an innovative SLIP-FALLS platform, …

Understanding Wavelet Analysis And Filters For Engineering Applications, Chethan Bangalore Parameswariah

Doctoral Dissertations

Wavelets are signal-processing tools that have been of interest due to their characteristics and properties. Clear understanding of wavelets and their properties are a key to successful applications. Many theoretical and application-oriented papers have been written. Yet the choice of a right wavelet for a given application is an ongoing quest that has not been satisfactorily answered. This research has successfully identified certain issues, and an effort has been made to provide an understanding of wavelets by studying the wavelet filters in terms of their pole-zero and magnitude-phase characteristics. The magnitude characteristics of these filters have flat responses in both …

Microreactor System With Immobilized Enzyme On Polydimethylsiloxane (Pdms) Polymers, Zonghuan Lu

Doctoral Dissertations

Microsystems, specifically microreactors, open the gate to new, improved analytical techniques while offering many advantages for a large number of applications in chemical engineering, pharmacy, medicine, and biotechnology. This study explored the feasibility of fabrication of microreactors using polydimethylsiloxane (PDMS) as a support for enzyme immobilization. Urease enzyme was used for catalyzing the conversion of urea to ammonia.

PDMS (polydimethylsiloxane) is a silicone-based elastomeric polymer. Traditional micromanufacturing technology was employed for reactor mold fabrication. The mold was fabricated based on photolithography techniques, and SU-8 photoresist was used to construct reactor structure templates. The resulting silicon-wafer based reactor molds were then …